Invention to a device for axially connecting a tube of composite material to metallic end pieces and more particularly to a device using the incorporation into the composite structure of a metallic ferrule serving as an anchoring piece for the end pieces.
The invention is more especially intended, among other applications to equip the landing gear of aerodynes particularly light aeroplanes or helicopters, the tubular columns of which, advantageously made of a composite material, have, on one hand, to withstand the internal pressure and, on the other hand, to resist axial tensile and compressive stresses.
In the field concerned with the connection of columns or shafts of composite materials to metallic end pieces, there have been proposed a certain number of solutions which can give satisfaction in specific applications but which remain inadequate for uses involving severe stresses, as is the case of the jacks and shock absorbers of landing gear tyres.
Document FR-A 2 434 300 describes a transmission shaft element of fiber reinforced plastic material in which there are provided means for ensuring interconnection between the shaft itself and the yoke of a universal joint that is efficient and adequate to withstand the forces of flexion and torque to which the element is subjected. For this purpose, the shaft is connected to a sleeve that is integral with the yoke via mechanical anchoring means constituted, for example, by an annular rib, possibly associated with other excrescences such as ridges, bosses or corrugations. Anchoring is effected from a rib provided on the end piece which bears on a corresponding impression provided on the tube. This known connection is only designed, however, to allow for bending stress and torque, and not tensile and compressive stresses.
According to document FR-A 2 343 918, it is known to make a control rod whose tubular body, composed of high strength fibers agglomerated by a polymerized synthetic resin, is made integral with a metallic end piece having external scores and corrugations. To obtain the rod, strips of suitable fibers encapsulated in unpolymerized epoxy resin, the fibers being parallel or in braids, are wound onto the mandrel of the tubular body, equipped with its metal end pieces. Several layers of fibers are wound on in this way, orientated in different directions. At the ends, the layers of fibers mate with the scores or corrugations; after polymerization, the binding of the fibers over the scored portions of the end pieces gives a rod whose end pieces very satisfactorily fixed to the tubular body and which is capable of withstanding tensile and compressive stresses.
There also exists another method of connection, as described in document U.S. Application No. 3 989 280, which consists in providing a connection between a pipe of composite material and a metallic pipe via a collar or a peripheral shoulder integral with a pipe and on which the other pipe is manufactured.
In all these solutions interference of form thus occurs, at a given point between the part made of composite material and a metallic end piece. Quite often, the metallic end piece therefore has to be given a special shape, with ribs for example, to be able to cooperate with the portion made of composite material. Sometimes, this type of connection makes it necessary for the metallic end piece or the composite tube to have an irregular inner or outer surface in the region of the ribs which can hinder the passage of sliding members. Apart from these drawbacks, the strength of these types of connection can prove inadequate for tubular columns subjected to severe tensile and compressive stresses, as is the case of hydro-pneumatic landing gear helicopters.